Resonant switching regulator with continuous current

ABSTRACT

A switched-mode power regulator circuit has four solid-state switches connected in series and a capacitor and an inductor that regulate power delivered to a load. The solid-state switches are operated such that a voltage at the load is regulated by repetitively (1) charging the capacitor causing an increase in current flow in the inductor followed by a decrease in current flow in the inductor and before the current flow in the inductor stops, (2) discharging the capacitor causing an increase in current flow in the inductor followed by a decrease in current flow in the inductor and before the current flow in the inductor stops, repeating (1).

FIELD

The present invention relates generally to switched-mode powerregulators and in particular to power regulators that operate at highfrequencies with high efficiency.

BACKGROUND

A wide variety of electronic devices are available for consumers today.Many of these devices have integrated circuits that are powered byregulated low voltage DC power sources. These low voltage power sourcesare often generated by dedicated power regulator circuits that use ahigher voltage input from a battery or another power source. In someapplications, the dedicated power regulator circuit can be one of thelargest power dissipating components of the electronic device and cansometimes consume more space than the integrated circuit that it powers.

As electronic devices become more sophisticated and more compact, thesize, the performance and the efficiency of the dedicated powerregulator circuits needs to be improved. Increased switching frequencyof the power regulator circuit has been one of the primary designadvances to address these competing requirements. Increased switchingfrequency reduces the size and typically the cost of the large passivecomponents (e.g., capacitors and inductors) while also enabling thepower regulator to respond to faster transient requirements. Thedifficulty with increased switching frequency is typically the increasedswitching losses associated with the increased number of switchingcycles (i.e., decreased efficiency). New methods of reducing the sizeand improving the efficiency of power regulator circuits are needed tomeet the needs of future electronic devices.

SUMMARY

In some embodiments a power conversion circuit comprises a firstterminal, a first solid-state switch having a pair of first switchterminals and a first control terminal wherein the pair of first switchterminals are connected between the first terminal and a first junction.A second solid-state switch has a pair of second switch terminals and asecond control terminal wherein the pair of second switch terminals areconnected between the first junction and a second junction. A thirdsolid-state switch has a pair of third switch terminals and a thirdcontrol terminal wherein the pair of third switch terminals areconnected between the second junction and a third junction. A fourthsolid-state switch has a pair of fourth switch terminals and a fourthcontrol terminal wherein the pair of fourth switch terminals areconnected between the third junction and a ground. A capacitor iscoupled between the first junction and the third junction, and aninductor is coupled between the second junction and a load. A controllertransmits control signals to control the first, second, third and fourthsolid-state switches through the first, second, third and fourth controlterminals, respectively, such that a voltage at the load is regulated byrepetitively (1) charging the capacitor causing an increase in currentflow in the inductor followed by a decrease in current flow in theinductor and before the current flow in the inductor stops, (2)discharging the capacitor causing an increase in current flow in theinductor followed by a decrease in current flow in the inductor andbefore the current flow in the inductor stops, repeating (1).

In some embodiments the power conversion circuit generates a firstpreflux condition in the inductor before (1). In various embodimentsduring the first preflux condition the first and the second solid-stateswitches are in an on state. In some embodiments a second prefluxcondition is generated in the inductor before (2). In variousembodiments during the second preflux condition the second and thefourth solid-state switches are in an on state.

In some embodiments after the decrease in current flow the inductor in(1) the first, the third and the fourth solid-state switches are in anon state. In various embodiments after the decrease in current flow theinductor in (2) the second, the third and the fourth solid-stateswitches are in an on state. In some embodiments when repetitivelyperforming (1) and (2) a continuous current flows through the inductor.

In some embodiments the controller allows the current flow in theinductor to stop in (1) and in response controls the first and thefourth solid-state switches into an on-state and the second and thirdsolid-state switches into an off state. In various embodiments thecontroller controls the first and the fourth solid-state switches intoan on-state and the second and third solid-state switches into an offstate in response to a voltage at the load being above a predeterminedthreshold voltage. In some embodiments the controller allows the currentflow in the inductor to stop in (2) and in response controls the secondand the third solid-state switches into an on-state and the first andfourth solid-state switches into an off state. In various embodimentsthe circuit is disposed on a unitary semiconductor die that includes theload.

In some embodiments a power conversion circuit comprises a firstterminal, a first solid-state switch having a pair of first switchterminals and a first control terminal wherein the pair of first switchterminals are connected between the first terminal and a first junction.A second solid-state switch having a pair of second switch terminals anda second control terminal wherein the pair of second switch terminalsareconnected between the first junction and a second junction. A thirdsolid-state switch having a pair of third switch terminals and a thirdcontrol terminal wherein the pair of third switch terminals areconnected between the second junction and a third junction. A fourthsolid-state switch having a pair of fourth switch terminals and a fourthcontrol terminal wherein the pair of fourth switch terminals areconnected between the third junction and a ground. A capacitor coupledbetween the first junction and the third junction, and an inductorcoupled between the second junction and a load. Wherein the first,second, third and fourth solid-state switches regulate a voltage at theload by repetitively (1) charging the capacitor causing an increase incurrent flow in the inductor followed by a decrease in current flow inthe inductor and before the current flow in the inductor reaches a firstlevel, and (2) discharging the capacitor causing an increase in currentflow in the inductor followed by a decrease in current flow in theinductor and before the current flow in the inductor reaches a secondlevel, repeating (1).

In some embodiments the first and the second levels are substantially 0amperes. In various embodiments a first preflux condition is generatedin the inductor before (1). In some embodiments a second prefluxcondition is generated in the inductor before (2). In variousembodiments when repetitively performing (1) and (2) a continuouscurrent flows through the inductor. In some embodiments in response to avoltage at the load being above a predetermined threshold voltage thecontroller allows the current flow in the inductor to stop in (1). Invarious embodiments the first, second, third and fourth solid-stateswitches are disposed on a unitary semiconductor die that is attached toa substrate having a plurality of contacts for forming electricalconnections to a circuit board.

In some embodiments a method of operating a power conversion circuit todeliver power to a load comprises supplying power to the powerconversion circuit with a power supply connected to a first terminal.The power conversion circuit comprises a first solid-state switch havinga pair of first switch terminals and a first control terminal whereinthe pair of first switch terminals are connected between the firstterminal and a first junction. A second solid-state switch having a pairof second switch terminals and a second control terminal wherein thepair of second switch terminals are connected between the first junctionand a second junction. A third solid-state switch having a pair of thirdswitch terminals and a third control terminal wherein the pair of thirdswitch terminals are connected between the second junction and a thirdjunction. A fourth solid-state switch having a pair of fourth switchterminals and a fourth control terminal wherein the pair of fourthswitch terminals are connected between the third junction and a ground.A capacitor coupled between the first junction and the third junction,and an inductor coupled between the second junction and the load and acontroller that controls on and off states of the first, second, thirdand fourth solid-state switches. The on and off states of the first, thesecond, the third and the fourth solid-state switches are controlledsuch that a voltage at the load is regulated by repetitively (1)charging the capacitor causing an increase in current flow in theinductor followed by a decrease in current flow in the inductor andbefore the current flow in the inductor reaches a first level, (2)discharging the capacitor causing an increase in current flow in theinductor followed by a decrease in current flow in the inductor andbefore the current flow in the inductor reaches a second level,repeating (1).

To better understand the nature and advantages of the present invention,reference should be made to the following description and theaccompanying figures. It is to be understood, however, that each of thefigures is provided for the purpose of illustration only and is notintended as a definition of the limits of the scope of the presentinvention. Also, as a general rule, and unless it is evident to thecontrary from the description, where elements in different figures useidentical reference numbers, the elements are generally either identicalor at least similar in function or purpose.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a unitary die containing a power regulatorportion and a load portion according to an embodiment of the invention;

FIG. 2 is a schematic of the switched regulation circuit that has beenremoved from the power regulator portion of the schematic in FIG. 1;

FIG. 3 is a flowchart of a repetitive switching sequence for theswitched regulation circuit in FIG. 2 according to an embodiment of theinvention;

FIG. 4 is a schematic of the switched regulation circuit shown in FIG. 2in a particular switch configuration according to the flowchart in FIG.3;

FIG. 5 is a schematic of the switched regulation circuit shown in FIG. 2in a particular switch configuration according to the flowchart in FIG.3;

FIG. 6 is a schematic of the switched regulation circuit shown in FIG. 2in a particular switch configuration according to the flowchart in FIG.3;

FIG. 7 is a schematic of the switched regulation circuit shown in FIG. 2in a particular switch configuration according to the flowchart in FIG.3;

FIG. 8 is a timing diagram of voltages and currents within the switchedregulation circuit of FIG. 2 according to the switching sequence in FIG.3;

FIG. 9 is a is a flowchart of a repetitive switching sequence for theswitched regulation circuit in FIG. 3 according to an embodiment of theinvention;

FIG. 10 is a schematic of the switched regulation circuit shown in FIG.2 in a particular switch configuration according to the flowchart inFIG. 9;

FIG. 11 is a schematic of the switched regulation circuit shown in FIG.2 in a particular switch configuration according to the flowchart inFIG. 9;

FIG. 12 is a schematic of a switched regulation circuit with parasiticelements according to an embodiment of the invention;

FIG. 13 is a schematic of the switched regulation circuit shown in FIG.2 with an added power supply coupled to the circuit with a pair ofswitches according to an embodiment of the invention;

FIG. 14 is a flowchart of a repetitive switching sequence for theswitched regulation circuit in FIG. 2 according to an embodiment of theinvention;

FIG. 15 is a timing diagram of voltages and currents within the switchedregulation circuit of FIG. 2 according to the switching sequence in FIG.14;

FIG. 16 is a timing diagram of voltages and currents within the switchedregulation circuit of FIG. 2 according to the switching sequence in FIG.14 including “soft braking”;

FIG. 17 is a method of controlling the preflux time with a variabletimer;

FIG. 18 is an alternative method of controlling the preflux time with avariable timer;

FIG. 19 is a flowchart of a repetitive switching sequence providing acontinuous current output for the switched regulation circuit in FIG. 2according to an embodiment of the invention;

FIG. 20 is a timing diagram of voltages and currents within the switchedregulation circuit of FIG. 2 according to the switching sequence in FIG.19;

FIG. 21 is a schematic of the switched regulation circuit shown in FIG.2 in a particular switch configuration according to the switchingsequence in FIG. 19;

FIG. 22 is a schematic of the switched regulation circuit shown in FIG.2 in a particular switch configuration according to the switchingsequence in FIG. 19;

FIG. 23 is a schematic of the switched regulation circuit shown in FIG.2 in a particular switch configuration according to the switchingsequence in FIG. 19;

FIG. 24 is a schematic of the switched regulation circuit shown in FIG.2 in a particular switch configuration according to the switchingsequence in FIG. 19;

FIG. 25 is a schematic of the switched regulation circuit shown in FIG.2 in a particular switch configuration according to the switchingsequence in FIG. 19;

FIG. 26 is a schematic of the switched regulation circuit shown in FIG.2 in a particular switch configuration according to the switchingsequence in FIG. 19; and

FIG. 27 is a flowchart of a example switching sequences for the switchedregulation circuit in FIG. 2 according to embodiments of the invention.

DETAILED DESCRIPTION

Certain embodiments of the present invention relate to power regulatorcircuits. While the present invention can be useful for a wide varietyof power regulator circuits, some embodiments of the invention areparticularly useful for power regulator circuits that can operate atrelatively high frequencies and high efficiencies enabling the circuitsto be completely contained on a unitary integrated circuit (IC) deviceadjacent to the load that it powers, as described in more detail below.

Now referring to FIG. 1 a non-limiting example block diagram of a powerregulator circuit and a load integrated on a unitary IC device isillustrated. Unitary IC 100 may have a power regulator portion 105 and aload portion 110 monolithically integrated. Load portion 110 may performany function including, but not limited to, a central processing unit, agraphics processing unit, an application processing unit, a displaydriver, or other function. Load portion 110 may be illustratedschematically by a load resistor 115.

Power regulator portion 105 may be configured to receive an inputvoltage from a first terminal 120 and supply a regulated output voltageto load 115. Power regulator portion 105 may have a switched regulationcircuit 125 that is operated and controlled by one or more peripheralcircuits, as discussed in more detail below.

Switched regulation circuit 125 may comprise four solid-state switchesconnected in series, an LC circuit and an output capacitor. Morespecifically, power regulation circuit 125 may be supplied with DC powerthrough first terminal 120. A first solid-state switch 130 has a pair offirst switch terminals 133 a, 133 b connected between first terminal 120and a first junction 135, respectively. First solid-state switch 130 mayalso have a first control terminal 137 that may be used to transitionthe first solid-state switch between an on state and an off state, asdiscussed in more detail below.

A second solid-state switch 140 has a pair of second switch terminals143 a, 143 b connected between first junction 135 and a second junction145, respectively. Second solid-state switch 140 further has a secondcontrol terminal 147. A third solid-state switch 150 has a pair of thirdswitch terminals 153 a, 153 b connected between second junction 145 anda third junction 155, respectively. Third solid-state switch further hasa third control terminal 157. Fourth solid-state switch 160 has a pairof fourth switch terminals 163 a, 163 b connected between third junction155 and a ground 165, respectively. Fourth solid-state switch 160further has a fourth control terminal 167. An LC circuit includes acapacitor 170 connected between first junction 135 and third junction155, and an inductor 173 connected between second junction 145 and load115. In further embodiments, inductor 173 may be in series withcapacitor 170. An output capacitor 175 is connected between inductor 173and load 115 and coupled to ground 165. An output node 176, to whichinductor 173, output capacitor 175 and load 115 are connected may beused to monitor an output voltage (Vout) of switched regulation circuit125. For ease of identification, labels M1, M2, M3 and M4 may be usedthroughout this disclosure to identify first solid-state switch 130,second solid-state switch 140, third solid-state switch 150 and fourthsolid-state switch 160, respectively. In some embodiments, the inductor173 can be located between the capacitor 170 and either node 135 or node155.

A controller is configured to receive inputs from the switchedregulation circuit and control the operation of the solid state switchesto provide a substantially constant output, as discussed in more detailbelow. Controller 180 may be coupled to driver circuits 183 with controllines 185(1) . . . 185(4) such that each control line controls theoperation of one solid-state switch. In one embodiment, controller 180may transmit high and low control signals through control lines 185(1) .. . 185(4) to operate a corresponding driver circuit 183. Drivercircuits 183 may be coupled to first, second, third and fourth controlterminals 137, 147, 157, 167, respectively of first, second, third andfourth solid state switches, 130, 140, 150, 160, respectively. Drivercircuits 183 may receive commands from controller 180 and control theoperation of first, second, third and fourth solid state switches, 130,140, 150, 160, respectively by sending signals through first, second,third and fourth control terminals 137, 147, 157, 167, respectively.Driver circuits 183 can have other functions, for example, convertingthe voltage level of the control circuitry to voltages for the drivers.

In some embodiments, controller 180 may regulate the voltage at outputnode 176 by controlling the first, second, third and fourth solid stateswitches, 130, 140, 150, 160, respectively, by repetitively (1) chargingcapacitor 170 causing a current to flow in inductor 173 and (2)discharging the capacitor causing current to flow in the inductor, asdiscussed in more detail below.

In some embodiments, one or more peripheral circuits may be employedindividually or in combination with each other to aid controller 180 inoperating switched regulation circuit 125. In one embodiment, a firstcomparator 187 may be connected from first terminal 120 to a first side181 of capacitor 170 and be configured to compare the respective voltagelevels. By comparing voltage levels, first comparator 187 may monitorthe current flowing through first solid-state switch 130 (i.e., zerovolts across the comparator equates to zero current flowing throughfirst solid state switch). Similarly, second comparator 190 may beconnected between ground 165 and a second side 191 of capacitor 170 andbe configured to detect current flowing through fourth solid-stateswitch 160. Thus, first and second comparators 187, 190, respectivelymay be used to monitor current flowing through inductor 173 when firstor fourth solid-state switches, 130, 160, respectively, are coupled inseries with the inductor, as described in further detail below. In someembodiments, first comparator 187 may be connected between terminals 120and 145 to detect current flowing through switches 130 and 140 (e.g., todetect preflux current). In some embodiments, second comparator 190 maybe connected between terminals 145 and 165 to detect current flowingthrough switches 150 and 160 (e.g. to detect softbrake current).

In another embodiment a third comparator 193 may be connected betweensecond junction 145 and a first voltage source 194. In one embodimentfirst voltage source 194 may be a ground connection (i.e., having apotential of 0 volts). In some embodiments, a voltage level of firstvoltage source 194 may be used to create a timing offset for controller180 to accommodate for delays in switch actuation. Third comparator 193may be used to detect the voltage at second junction 145 when it isequivalent to the voltage of first voltage source 194 Similarly, fourthcomparator 195 may be connected between output node 176 (Vout) and asecond voltage source 196 such that it notifies controller 180 when itdetects that Vout is equivalent to the second voltage source. Secondvoltage source 196 may also be adjusted to compensate for switchactuation delays. The combination of first, second, third and fourthcomparators, 187, 190, 193, 195, respectively, may be used to aidcontroller 180 in detecting the current in inductor 173, the voltageacross capacitor 170, and the voltage at output node 176 (Vout). Inother embodiments different methods may be used to detect voltages andcurrents in switched regulation circuit 125 without departing from thisinvention. For example, in one embodiment a voltage across inductor 173may be used to detect current in the inductor.

Although FIG. 1 illustrates a unitary IC 100 with all componentsintegrated within the unitary IC, other embodiments may have thecomponents disposed on more than one IC, while further embodiments mayhave one or more components that are not on an IC and disposed oncircuitry adjacent the IC. For example, one embodiment may have outputcapacitor 175 or inductor 173 disposed adjacent one or more ICs. Inother embodiments, one or more switches or drivers or control circuitsmay be on a separate IC.

Now referring to FIG. 2, for simplicity of illustration, switchedregulation circuit 125 has been removed from power regulator portion 105of unitary IC device 100 shown in FIG. 1. Switched regulation circuit125 will be used to show the repetitive switching sequence used by thepower regulator to control the voltage at output node 176 (Vout)delivered to load 115 (see FIG. 1).

Now referring simultaneously to FIGS. 3-8 a first embodiment of aswitching sequence and timing diagram for switched regulation circuit125 is illustrated. FIG. 3 identifies four different solid-state switchconfigurations, the order in which the solid-state switches are turnedon and off and the decisions between each step. FIGS. 4-7 illustratesimplified circuit schematics of each of the four different solid-stateswitch configurations. Solid-state switches in the on state are depictedwith solid lines and solid-state switches that are in the off state aredepicted with dashed lines. FIG. 8 illustrates an example timingdiagram, showing the control signals delivered to each of the foursolid-state switches as well as the voltage at second junction 145, thecurrent within inductor 173, an inductor current comparator output andthe voltage across capacitor 173. The switching sequence illustrated inFIGS. 3-8 is only an example and other sequences, timings andconfigurations are within the scope of this disclosure.

Now referring to FIG. 3, a first switching sequence 300 havingsequential steps 305 through 360 is illustrated. In step 305, second andthird solid-state switches M2, M3, respectively, are controlled to be inan on state and first and fourth solid-state switches M1, M4 arecontrolled to be in an off state. A simplified schematic of switchedregulation circuit 125 in step 305 is illustrated in FIG. 4. Second andthird solid-state switches 140, 150, respectively are in an on state(solid lines) and first and fourth solid-state switches 130, 160,respectively are in an off state (dashed lines). Therefore, capacitor170 is in a shorted condition, allowing any residual charge within thecapacitor to dissipate such that the capacitor is discharged.

Now referring to timing diagram 800 in FIG. 8, first step 305 occurs attime t1. Trace 805 illustrates a control voltage applied to firstsolid-state switch 130. In the particular embodiment depicted in diagram800, switches are turned on when approximately 1 volt is applied. Attime t1 trace 805 is at approximately 0 volts thus first solid-stateswitch 130 is off. Trace 810 illustrates a control terminal voltageapplied to second solid-state switch 140. At time t1 trace 810 is atapproximately 1 volt thus second solid-state switch is on. Trace 815illustrates a control terminal voltage applied to third solid-stateswitch 150. At time t1 trace 815 transitions to approximately 1 voltthus third solid-state switch 150 transitions from off to on. Trace 820illustrates a control terminal voltage applied to fourth solid-stateswitch 160. At time t1 trace 820 is at approximately 0 volts thus fourthsolid-state switch is off.

Trace 825 illustrates a voltage at second junction 145. At time t1,capacitor 170 is shorted. Trace 830 illustrates current through inductor173. At time t1 inductor 173 is decoupled from the remainder of switchedregulation circuit 125 thus the current in inductor 173 is zero. Trace835 illustrates a comparator output corresponding to a zero currentcondition in inductor 173, as discussed in more detail below. Trace 840illustrates the voltage across capacitor 170. At time t1 capacitor 170is shorted causing the voltage across capacitor 173 to decrease as thecapacitor is discharged.

Now referring back to FIGS. 3 and 4, after the controller sets thesolid-state switches to their respective states identified in step 305,it advances to step 310 were it detects the voltage at output node 176(Vout). In some embodiments Vout may be detected using comparator 195(see FIG. 1) as discussed above, or by any other method. Advancing tostep 315 the controller may detect if the voltage at output node 176 hasdecreased below a first threshold voltage (V_(TH1)). If Vout remainsabove V_(TH1) then the controller continues to detect Vout (i.e.,returns to step 310) until Vout drops below V_(TH1). In some embodimentsthe controller may cyclically detect Vout then compare it to V_(TH1),while in other embodiments the controller may respond to a signal, suchas from a comparator, that Vout has decreased below V_(TH1). Myriadmethods may be used to detect Vout, compare it to V_(TH1) and notify thecontroller.

Now referring back to FIG. 3, step 315, once Vout drops below V_(TH1)the controller advances to step 320 where third solid-state switch M3remains on while first solid-state switch M1 is turned on simultaneouslywith turning second solid-state switch M2 off. Thus, first and thirdsolid-state switches, M1, M3, respectively, are on while second andfourth solid-state switches M2, M4, respectively, are off. A simplifiedschematic of switched regulation circuit 125 in step 320 is illustratedin FIG. 5. In this state the voltage at first terminal 120 (Vin) isapplied directly to second junction 145. Capacitor 170 was fullydischarged in the previous step and now begins to charge. Capacitor 170charges with a time constant set by capacitor 170 and inductor 173values. Further, as capacitor 170 begins to charge, current flow ininductor 173 increases as the voltage between 145 and the output ispositive.

Step 320 is illustrated in timing diagram 800 (see FIG. 8) at time t2.Now referring simultaneously to FIGS. 5 and 8, at time t2, firstsolid-state switch 130 (i.e., trace 805) turns on almost simultaneouslywith second solid-state switch 140 (i.e., trace 810) turning off. Thevoltage at second junction 145 (i.e., trace 825) increases rapidly tothe voltage at first terminal 120 (Vin), in this application (orembodiment) approximately 2 volts. Between time t1 and t2 the voltage atsecond junction 145 may fluctuate At time t2, current in inductor 173(i.e., trace 830) begins to increase. As capacitor 170 becomes charged(i.e., trace 840 approaches 2 volts), Voltage at 145 start to decrease.When the voltage at 145 goes below the load voltage 176, the current ininductor 173 (i.e., trace 830) starts to decrease. Thus, in step 320capacitor 170 becomes charged, causing a current to flow in inductor173, and increasing the voltage at output node 176 (Vout). Thecontroller then proceeds to step 325 (see FIG. 3).

In step 325, the current in inductor 173 (L_(I)) is detected. In someembodiments the current may be detected as illustrated in FIG. 1 withcomparator 187. In one embodiment comparator 187 monitors current flowthrough first solid-state switch 130 by comparing a voltage differencebetween first terminal 120 and first side 181 of capacitor 170. As thevoltage difference decreases, the current commensurately decreases inboth first solid-state switch 130 and inductor 173. Referring now tostep 330 in FIG. 3, once current in inductor 173 is approximately equalto zero, the controller proceeds to step 335 where first and thirdsolid-state switches M1, M3, respectively, turn off and fourthsolid-state switch M4 turns on while second solid-state switch M2remains off. As discussed above, since the transition to step 335 onlyoccurs when the current in inductor 176 is approximately zero, thetransition to step 335 may employ zero current switching of firstsolid-state switch M1. Zero current switching occurs when the currentthrough the solid-state switch is approximately zero, before changingthe state of the switch. This reduces switching losses, reduces inputsupply noise, and improves the efficiency of switched regulation circuit125, as discussed in more detail below.

Continuing to refer to step 335 in FIG. 3, in some embodiments theswitching transitions may occur simultaneously while in otherembodiments there may be slight delays between switch transitions. Asimplified schematic of switched regulation circuit 125 in step 335 isillustrated in FIG. 6. Fourth solid-state switch 160 ties second side191 of capacitor 170 to ground, however first side 181 of the capacitoris left floating such that the capacitor remains charged. Thisconfiguration is essentially an off state, where the system issubstantially at steady-state. Other embodiments may have a differentoff state configuration. In one embodiment, all solid-state switches maybe in an off position, while in further embodiments third solid-stateswitch 150 may be the only switch in an on state which connectscapacitor 170 to inductor 173. In another embodiment both first andfourth solid-state switches 130, 160, respectively may be onsimultaneously. Other off state solid-state switch configurations arewithin the scope of this disclosure.

Step 335 of FIG. 3 is illustrated in timing diagram 800 of FIG. 8, attime t3. Now referring simultaneously to FIGS. 6 and 8, at time t3 firstand third solid-state switches, 130, 150, respectively, turn off andfourth solid-state switch 160 turns on while second solid-state switch140 remains off. After the switching transitions, second junction 145(i.e., trace 825) is disconnected from the solid-state switches and itsvoltage starts to increase. Capacitor 170 (i.e., trace 840) remainscharged and the current in inductor 173 (i.e., trace 830) remains nearzero. In step 340 the voltage at output node 176 (Vout) may be detectedwith comparator 195 (see FIG. 1) as discussed above in step 310. Inother embodiments, Vout may be detected using a different method. Asshown in step 345, the controller advances to step 350 when Vout dropsbelow a second threshold voltage (V_(TH2)).

Now referring to FIG. 3, step 350, fourth solid-state switch M4 remainson and second solid-state switch M2 is turned on while first and thirdsolid-state switches M1, M3, respectively, remain off. A simplifiedschematic of switched regulation circuit 125 in step 350 is illustratedin FIG. 7. Capacitor 170 is connected between inductor 173 and ground165, allowing the charge stored in the capacitor to discharge throughthe inductor to load 115 (see FIG. 1). As capacitor 170 begins todischarge (with a time constant set by capacitor 170 and inductor 173),current in inductor 173 starts to increase and voltage at output node176 (Vout) increases. This condition is illustrated in timing diagram800 in FIG. 8 at time t4.

Now simultaneously referring to FIGS. 7 and 8, at time t4 secondsolid-state switch 140 (i.e., trace 810) turns on. The voltage at secondjunction 145 (i.e., trace 825) makes an adjustment to approximately 2volts as it is connected to fully charged capacitor 170. As capacitor170 resonates with inductor 173, it discharges (i.e., trace 840) causingcurrent to increase in inductor 173 (i.e., trace 830). This causes thevoltage at Vout to increase. As the charge in capacitor 170 is reduced,current in inductor 173 decreases (i.e., trace 830). After configuringthe solid-state switches, controller advances to steps 355 and 360 (seeFIG. 3).

In step 355, the current in inductor 173 is detected. In someembodiments the current may be detected as illustrated in FIG. 1 withcomparator 190. In further embodiments, comparator 190 (see FIG. 1) maybe used to monitor the current through fourth semiconductor switch 160and indirectly through inductor 173, by detecting a voltage differentialbetween ground 165 and second side 191 of capacitor 170. For example, attime t5 in timing diagram 800 in FIG. 8, trace 835 illustrates acomparator output corresponding to a zero current condition in inductor173. In other embodiments different methods may be used to detectcurrent in inductor 173.

Referring now simultaneously to FIGS. 3 and 7, in step 360, once thecurrent in inductor 173 is approximately equal to zero, the controllerproceeds back to step 305, where third solid-state switch M3 is turnedon and second solid-state switch M2 remains on while first solid-stateswitch M1 remains off and fourth solid-state switch M4 is turned off.Thus, M2 and M3 are on while M1 and M4 are off. This configurationshorts capacitor 170, repeating the entire switching sequence 300. Asdiscussed above, since the current in inductor 173 and fourthsolid-state switch M4 is at or near zero during the transition from step360 to 305, zero current switching methods may be used to decreaseswitching losses, reduce input supply noise and improve efficiency, asdiscussed in more detail below.

In the particular switching sequence illustrated in FIG. 3, eachsolid-state switch turns on and off only once during each repetitiveswitching cycle. Such a sequence may enable improved efficiency byminimizing switching losses. In other embodiments, different switchingconfigurations and sequences may be used where one or more switches maybe turned on and off more than once.

As discussed above in FIG. 1, power regulator portion 105 and a loadportion 110 may be monolithically integrated on unitary IC 100. In oneembodiment unitary IC 100 may comprise silicon and first, second, thirdand fourth solid-state switches 130, 140, 150, 160 may be junction gatefield effect devices (JFETs) while in other embodiments they may bemetal-oxide semiconductor field-effect transistors (MOSFETs), bi-polardevices or any other type of solid-state transistor. In furtherembodiments other materials may be used for unitary IC 100 such assilicon-germanium, silicon-carbide, gallium-nitride, gallium-arsenideand other materials. In one embodiment, unitary IC 100 may use a 28 nmand 40 nm fabrication process with an on die inductor in the range of1-5 nH and an on die capacitor in the range of 100-300 pF, resulting inan on-time in the range of 1-5 ns.

In further embodiments, although solid-state switches 130, 140, 150 and160 may be referred to in singular form, in some embodiments one or moreof them may comprise more than one switch. More specifically, in oneembodiment first solid state switch M1 may be made from two solid-stateswitches connected in series. In other embodiments one or more of thesolid-state switches may comprise two or more solid-state switches thatoperate in conjunction with one another.

Now referring to FIG. 9 another embodiment of a sequential switchingsequence 900 is illustrated. Sequence 900 has many similar steps assequence 300 in FIG. 3 such as steps 305-325 and 335-355. Thus stepsthat are the same between the sequences use the same reference numbersand the same schematics in FIGS. 4-7. However, sequence 900 has addedsteps including two added switch configurations, steps 328 and 358, theschematics for which are illustrated in FIGS. 10 and 11. Reference willnow be made simultaneously to FIGS. 4-7 and 9-11.

Now referring to FIG. 9, a second switching sequence 900 havingsequential steps 305 through 361 is illustrated. In step 305, second andthird solid-state switches M2, M3, respectively, are controlled to be inan on state and first and fourth solid-state switches M1, M4 arecontrolled to be in an off state. A simplified schematic of switchedregulation circuit 125 in step 305 is illustrated in FIG. 4. Second andthird solid-state switches 140, 150, respectively are in an on state(solid lines) and first and fourth solid-state switches 130, 160,respectively are in an off state (dashed lines). Therefore, capacitor170 is in a shorted condition, allowing any residual charge within thecapacitor to dissipate such that the capacitor is discharged.

Now referring back to FIGS. 3 and 4, after the controller sets thesolid-state switches to their respective states identified in step 305,it advances to step 310 were it detects the voltage at output node 176(Vout). In some embodiments the voltage at output node 176 (Vout) may bedetected using comparator 195 (see FIG. 1) as discussed above, or by anyother method. Advancing to step 315 the controller may detect if thevoltage at output node 176 has decreased below a first threshold voltage(V_(TH1)). If Vout remains above V_(TH1) then the controller continuesto detect Vout (i.e., returns to step 310) until Vout drops belowV_(TH1). In some embodiments the controller may cyclically detect Voutthen compare it to V_(TH1), while in other embodiments the controllermay respond to a signal, such as from a comparator, that Vout hasdecreased below V_(TH1) and respond accordingly. Myriad methods may beused to detect Vout, compare it to V_(TH1) and notify the controller.

Now referring back to FIG. 9, step 315, once Vout drops below V_(TH1)the controller advances to step 320 where third solid-state switch M3remains on while first solid-state switch M1 is turned on simultaneouslywith turning second solid-state switch M2 off. Thus, first and thirdsolid-state switches, M1, M3, respectively, are on while second andfourth solid-state switches M2, M4, respectively, are off. A simplifiedschematic of switched regulation circuit 125 in step 320 is illustratedin FIG. 5. In this state the voltage at first terminal 120 (Vin) isapplied directly to second junction 145. Capacitor 170 was fullydischarged in the previous step and now begins to charge. Capacitor 170charges with a time constant set by capacitor 170 and inductor 173values. Further, as capacitor 170 begins to charge, current flow ininductor 173 increases then decrease.

In some embodiments, steps 325 and 326 may occur simultaneously usingone or more comparators or other techniques, as discussed in more detailbelow. In step 325, the current in inductor 173 (L₁) is detected. Insome embodiments this may be performed as illustrated in FIG. 1 withcomparator 187. In one embodiment comparator 187 monitors current flowthrough first solid-state switch 130 by comparing a voltage differencebetween first terminal 120 and first side 181 of capacitor 170. As thevoltage difference decreases, the current commensurately decreases inboth first solid-state switch 130 and inductor 173. In step 326 thevoltage drop across capacitor 170 (V_(CAP)) is detected, using one ormore comparators, as discussed above. More specifically the controlleris configured to continue charging the capacitor until a voltagepotential on the second junction is approximately 0 volts. In step 327the controller determines if the voltage on capacitor (V_(CAP)) 170 isequivalent to the voltage at (Vin) 120 before current in inductor 173 iszero. More specifically, during steps 320, 325, 326 and 327, capacitor170 is being charged and once it reaches full charge (i.e., voltage oncapacitor 170 is equivalent to the voltage at (Vin) 120 the controllerdetermines if there is still current flowing in inductor 170. If thereis still current in inductor 170, the controller proceeds to step 328,however it there is no current in the inductor then it proceeds to step335.

Proceeding now to step 328, assuming the condition L_(I)>0 whenV_(CAP)=Vin, first and third solid-state switches M1, M3 remain on whilefourth solid-state switch M4 is turned on simultaneously with turningsecond solid-state switch M2 off. Thus, first, third and fourthsolid-state switches, M1, M3 and M4, respectively, are on while secondsolid-state switch M2 is off. In some embodiments, M4 may be turned onslowly so that the current in M1 is slowly reduced so as to reduce theamount of supply noise. A simplified schematic of switched regulationcircuit 125 in step 328 is illustrated in FIG. 10. In this stateinductor 173 is shorted to ground 165, resulting in a discharge of anyremaining current within it. After configuring the solid-state switches,controller advances to steps 329 and 331 (see FIG. 9).

In step 329, the current in inductor 173 is detected. In someembodiments the current may be detected as illustrated in FIG. 1 withcomparator 190. In some embodiments, comparator 190 (see FIG. 1) may beused to monitor the current through fourth semiconductor switch 160 andindirectly through inductor 173, by detecting a voltage differentialbetween ground 165 and second side 191 of capacitor 170. In otherembodiments different methods may be used to detect current in inductor173.

Referring now simultaneously to FIGS. 3 and 7, in step 331, once thecurrent in inductor 173 is approximately equal to zero, the controllerproceeds to step 335. In summary, steps 328, 329 and 331 discharge theremaining current in inductor 170 and transition to the waiting state instep 335.

Referring now back to step 327, assuming condition L_(I)=0 (i.e., thereis no current in inductor 170), instead of going to step 328, thecontroller goes directly to step 335 where first and third solid-stateswitches M1, M3, respectively, turn off and fourth solid-state switch M4turns on while second solid-state switch M2 remains off. Thus, M4 is onwhile M1, M2 and M3 are off. As discussed above, since the transition tostep 335 only occurs when the current in inductor 176 is approximatelyzero, the transition to step 335 may employ zero current switching offirst solid-state switch M1. Zero current switching occurs when thecurrent through the solid-state switch is approximately zero, beforechanging the state of the switch. This reduces switching losses, reducesinput supply noise and improves the efficiency of switched regulationcircuit 125, as discussed in more detail below.

Continuing to refer to step 335 in FIG. 9, in some embodiments theswitching transitions may occur simultaneously while in otherembodiments there may be slight delays between switch transitions. Asimplified schematic of switched regulation circuit 125 in step 335 isillustrated in FIG. 6. Fourth solid-state switch 160 ties second side191 of capacitor 170 to ground, however first side 181 of the capacitoris left floating such that capacitor remains charged. This configurationis essentially an off state, where the system is substantially atsteady-state. Other embodiments may have a different off stateconfiguration. In one embodiment, all solid-state switches may be in anoff position, while in further embodiments third solid-state switch 150may be the only switch in an on state which connects capacitor 170 toinductor 173. In another embodiment both first and fourth solid-stateswitches 130, 160, respectively may be on simultaneously. Other offstate solid-state switch configurations are within the scope of thisdisclosure.

After the switches are configured in step 335 the controller advances tostep 340 where the voltage at output node 176 (Vout) may be detectedwith comparator 195 (see FIG. 1) as discussed above in step 310. Inother embodiments, Vout may be detected using a different method. Asshown in step 345, the controller advances to step 350 when the voltageat output node 176 (Vout) drops below a second threshold voltage(V_(TH2)).

Now referring to FIG. 9, step 350, fourth solid-state switch M4 remainson and second solid-state switch M2 is turned on while first and thirdsolid-state switches M1, M3, respectively, remain off. A simplifiedschematic of switched regulation circuit 125 in step 350 is illustratedin FIG. 7. Capacitor 170 is connected between inductor 173 and ground165, allowing the charge stored in the capacitor to discharge throughthe inductor to load 115 (see FIG. 1). As capacitor 170 begins todischarge (with a time constant set by capacitor 170 and inductor 173),current in inductor 173 starts to increase and voltage at output node176 (Vout) increases.

In some embodiments, steps 355 and 356 may occur simultaneously. Afterconfiguring the solid-state switches, the controller advances to step355 where the current in inductor 173 is detected and 356 where thevoltage drop across capacitor 170 (V_(CAP)) is detected, as discussedabove. More specifically, in one embodiment controller may continuedischarging the capacitor until a voltage potential on the secondjunction is approximately 0 volts. Then, in step 357 the controllerdetermines if the voltage across capacitor (V_(CAP)) 170 is zero voltsbefore current in inductor 173 is zero. More specifically, during steps350, 355, 356 and 357, capacitor 170 is being discharged and once itreaches near zero charge the controller determines if there is stillcurrent flowing in inductor 170. If there is no current in inductor 170,the controller proceeds back to the beginning of the switching sequence,step 305. However, if there is still current in inductor 170 then thecontroller proceeds to step 358.

Proceeding now to step 358, assuming the condition L₁>0 when V_(CAP)=0volts (i.e., there is still current in the inductor when the capacitoris discharged), second and fourth solid-state switches M2, M4,respectively, remain on while third solid-state switch M3 is turned onand first solid-state switch M1 is off. Thus, second, third and fourthsolid-state switches, M2, M3 and M4 respectively, are on while firstsolid-state switch M1 is off. A simplified schematic of switchedregulation circuit 125 in step 358 is illustrated in FIG. 11. In thisstate inductor 173 is shorted to ground 165, resulting in discharge ofany remaining current within it. After configuring the solid-stateswitches, controller advances to steps 359 and 361 (see FIG. 9).

In step 359, the current in inductor 173 is detected. In someembodiments the current may be detected as illustrated in FIG. 1 withcomparator 190. In some embodiments, comparator 190 (see FIG. 1) may beused to monitor the current through fourth semiconductor switch 160 andindirectly through inductor 173, by detecting a voltage differentialbetween ground 165 and second side 191 of capacitor 170. In otherembodiments different methods may be used to detect current in inductor173.

Referring now simultaneously to FIGS. 7 and 9, in step 361, once thecurrent in inductor 173 is approximately equal to zero, the controllerproceeds back to step 305, where third solid-state switch M3 is turnedon and second solid-state switch M2 remains on while first solid-stateswitch M1 remains off and fourth solid-state switch M4 is turned off.Thus, M2 and M3 are on while M1 and M4 are off. This configurationshorts capacitor 170, repeating the entire switching sequence 900. Asdiscussed above, since the current in inductor 173 and fourthsolid-state switch M4 is zero during the transition from step 361 to305, zero current switching methods may be used to decrease switchinglosses, reduce input supply noise and improve efficiency, as discussedin more detail below.

In the particular switching sequence illustrated in FIG. 9, eachsolid-state switch turns on and off only once during each repetitiveswitching cycle. Such a sequence may enable improved efficiency byminimizing switching losses. In other embodiments, different switchingconfigurations and sequences may be used where one or more switches maybe turned on and off more than once. Other embodiments may use switchingsequences where one or more on the solid-state switches are turned onand off more than once per switching cycle.

Some embodiments may employ one or more comparators such as comparators187, 190, 193, 195 in FIG. 1 to provide information to the controller tooperate switched regulation circuit 125 (see FIG. 1). Furtherembodiments may use a combination of comparators and timers to operateswitched regulation circuit 125. More specifically, with knowledge ofcertain switched regulation circuit 125 parameters reasonably accuratetimers may be used in the place of comparators to trigger the controllerto change switch configurations. In one embodiment, with knowledge ofone or more electrical characteristics of switched regulation circuit125, such as for example, Vin, Vout, inductance of inductor 17 orcapacitance of capacitor 170, one or more timers may be used to estimateone or more electrical characteristics of the switched regulationcircuit, such as for example current in inductor or voltage oncapacitor, and trigger the transitions between switch configurations. Insome embodiments, timers may be faster and easier to implement thancomparators. In one embodiment, only one comparator may be used to lookat Vout, and timers may be used for all other transitions.

Multiple circuit characteristics are discussed above and as discussedone or more of these characteristics may be used to determine when tochange a state of the switches such as, but not limited to, Vcap, Vout,Vin and Li. In such embodiments the circuit characteristics may becontinuously monitored and decisions may be made at particular timesduring each switch sequence as noted in the flow charts. Further, thewaveforms shown in the timing diagrams, such as FIG. 8 are forillustration only and the actual waveforms may be different.

As discussed above, in some switching transitions zero current switchingmay be used. As used herein, zero current switching means that thesolid-state switch may be turned off only when the current runningthrough the switch is at or near zero. Switching losses (i.e., turning aswitch off while it is conducting current or turning a switch on when ithas a voltage potential across it) may be a significant contributor topower loss in the system. Thus, the use of zero current switching mayresult in reduced switching losses, increased frequency of operation andin some embodiments, reduced electromagnetic interference (EMI)generation, as discussed in more detail below.

Now referring to FIG. 12, in some embodiments zero current switching andthe solid-state switching transition speed may be reduced to suppressinput supply noise (i.e., a type of EMI) as described in more detailbelow. FIG. 12 shows a simplified schematic 1200 of a power regulatorcircuit 1205 containing FETs and other circuitry that is powered by aninput supply 1210 (Vin) and grounded to a ground terminal 1215. In oneembodiment, power regulator circuit 1205 may be disposed on a unitarydie that is encapsulated in a semiconductor package. First and secondinductors 1220 a, 1220 b, respectively, represent the parasiticinductance associated with the power connections to power regulatorcircuit 1205. Parasitic inductance may result from traces on a circuitboard, interconnects within an electronic package, wire bonds to a die,traces on an integrated circuit or any other conductor. Capacitor 1225 arepresents parasitic capacitance between the power supply lines on thesupply side and capacitor 1225 b represents parasitic capacitancebetween the input and the output power supply lines on the receivingside.

During operation of power regulator circuit 1205, first and secondparasitic inductors 1220 a, 1220 b, respectively, cannot immediatelycease carrying current when the power regulator stops drawing currentfrom input supply 1210 (Vin), such as for example when M1 (see FIG. 1)switches off. When M1 shuts off abruptly while carrying current, theresidual energy within first and second parasitic inductors 1220 a, 1220b, may ring with one or more components within power regulator circuit1205.

To minimize or reduce the ringing (i.e., input supply noise), zerocurrent switching may be used, where the current in first and secondparasitic inductors 1220 a, 1220 b, respectively is brought to near zerobefore turning off M1. Such transitions are described in more detailabove where current in the circuit may be detected and the switch isoperated once the current has decayed to approximately zero. In otherembodiments, the abrupt transition from carrying current through M1 toM1 opening and immediately ceasing carrying current may be slowed, bytransitioning M1 more slowly from the on state to the off state. Morespecifically, in one embodiment if there is residual current in inductor173, M4 may be turned on to dissipate the current in the inductor.However, if the current transitions too quickly from M1 to M4 noise maybe created in the system. Thus, in some embodiments M4 may be turned onrelatively slowly so the current may slowly transition from goingthrough M1 to going through M4, creating a “quieter” switchingtransition. In one example embodiment, a transistor may be fabricatedwith a 28 nm process having a normal solid-state switching transitionspeed of approximately 10 ps. To reduce ringing, in one embodiment aslowed transition may be approximately ten times slower at 100 ps. Infurther embodiments the slowed transition may be between five times andfifteen times slower. In other embodiments, the slowed transition may bebetween 3 times and 17 times slower, as compared to a normal transitiontime. The slower transition turning M1 off may allow the current beslowly reduced in first and second parasitic inductors 1220 a, 1220 b,such that the ringing with on chip components is minimized oreliminated.

In further embodiments, zero current switching and the power regulationcircuits disclosed herein may enable switching speeds that operatebetween 1 MHz and 500 MHz. In other embodiments the switching speed maybe between 50 MHz and 200 MHz. In further embodiments the switchingspeed may be approximately 100 MHz.

Now referring to FIG. 13, in further embodiments a boost circuit 1300may be made by combining switched regulation circuit 125 with a powersupply 1305 that is coupled to capacitor 170 with first and secondsolid-state switches 1310 a, 1310 b, respectively. In this embodimentcapacitor 170 may be precharged by power supply 1305 such that when thecapacitor is connected to input terminal 120 (Vin) it acts like abattery and increases or decreases the voltage potential supplied toswitched regulation circuit 125. In one example embodiment, capacitor170 may be precharged to −2 volts, such that when the switching sequencestarts and the capacitor and inductor are connected to first terminal120 (Vin) at 2.5 volts, a potential of 4.5 volts is applied to thecapacitor and the inductor.

More specifically, referring to FIG. 3, step 305 and FIG. 9, step 305,instead of shorting capacitor 170 and completely discharging it, thecapacitor may alternatively be coupled to power supply 1305 where it isprecharged, such that in step 320 in FIGS. 3 and 9 when the capacitor isconnected to Vin, the voltage applied to capacitor 170 and inductor 176may be higher than Vin. In other embodiments the precharging may be usedto increase the range of switched regulation circuit 125 when notoperating under boost. Other configurations and variations of switchedregulation circuit 125 and methods of precharging the capacitor arewithin the scope of this disclosure. For example, in one embodiment thepower supply that is used for the precharging may be located on the samedie as switched regulation circuit 125. In some embodiments the powersupply may be a low drop out regulator, a switched capacitor or aswitching regulator that are on the same die. In other embodiments thepower supply may not be located on the same die as switched regulationcircuit 125.

Regulator with Inductor Preflux

In another embodiment a switched regulation circuit 125 (see FIG. 2) maybe configured to preflux the inductor 173 such that the switchedregulation circuit may deliver an increased output voltage and/orincreased output current, as discussed in more detail below.

Now referring simultaneously to FIGS. 2, 14 and 15 an embodiment of aswitching sequence and timing diagram for switched regulation circuit125 with inductor preflux is illustrated. More specifically, FIG. 2illustrates a simplified schematic of the switched regulation circuit125, FIG. 14 illustrates a switching sequence 1400 having sequentialsteps 1405 through 1460 for the four switches in switched regulationcircuit and FIG. 15 illustrates an example timing diagram, showing thecontrol signals delivered to each of the four solid-state switches aswell as the voltage at second junction 145, the current within inductor173 (I_(L)), and the voltage across capacitor 170 (V₁₃₅-V₁₅₅). Theswitching sequence illustrated in FIGS. 14 and 15 is for example onlyand other sequences, timings and configurations are within the scope ofthis disclosure.

Now referring to FIG. 14, a switching sequence 1400 having sequentialsteps 1405 through 1460 is illustrated. In step 1405, second and thirdsolid-state switches M2, M3, respectively, are controlled to be in an onstate and first and fourth solid-state switches M1, M4 are controlled tobe in an off state. Capacitor 170 is in a shorted condition, allowingany residual charge within the capacitor to dissipate such that thecapacitor is discharged.

Example currents and voltages within switched regulation circuit 125 forstep 1405 are illustrated in timing diagram 1500 in FIG. 15. For signalsM1, M2, M3, M4, the logic levels are indicated. A logic high level(sometimes noted as 1) indicates the switch (or composite switch) is on,a logic low (sometimes noted as 0) indicates the switch is off. Firststep 1405 occurs at time t1. Trace 1505 illustrates a control signalapplied to first solid-state switch 130. In the particular embodimentdepicted in diagram 1500, switches are turned on when approximately 1volt is applied. At time t1 trace 1505 is at approximately 0 volts thusfirst solid-state switch 130 is off. Trace 1510 illustrates a controlterminal voltage applied to second solid-state switch 140. At time t1trace 1510 is at approximately 1 volt thus second solid-state switch ison. Trace 1515 illustrates a control terminal voltage applied to thirdsolid-state switch 150. At time t1 trace 1515 is approximately 1 voltthus third solid-state switch 150 is on. Trace 1520 illustrates acontrol terminal voltage applied to fourth solid-state switch 160. Attime t1 trace 1520 is at approximately 0 volts thus fourth solid-stateswitch is off.

Trace 1525 illustrates a voltage at second junction 145. At time t1,inductor current (I_(L)) is approximately zero and capacitor 170 isshorted so second junction 145 is approximately at a voltage of (Vout)176. Trace 1530 illustrates current through inductor 173. At time t1inductor 173 is decoupled from the remainder of switched regulationcircuit 125 thus the current in inductor 173 is approximately zero.Trace 1540 illustrates the voltage across capacitor 170. At time t1capacitor 170 is shorted causing the voltage across capacitor 173 todecrease to approximately zero volts as the capacitor is discharged.

Now referring back to FIG. 14, after the controller sets the solid-stateswitches to their respective states identified in step 1405, it advancesto step 1410 were it detects the voltage at output node 176 (Vout). Insome embodiments Vout may be detected using comparator 195 (see FIG. 1)as discussed above, or by any other method. Advancing to step 1415 thecontroller may detect if the voltage at output node 176 has decreasedbelow a first threshold voltage (V_(TH1)). If Vout remains above V_(TH1)then the controller continues to detect Vout (i.e., returns to step1410) until Vout drops below V_(TH1). In some embodiments the controllermay cyclically detect Vout then compare it to V_(TH1), while in otherembodiments the controller may respond to a signal, such as from acomparator, that Vout has decreased below V_(TH1). Myriad methods may beused to detect Vout, compare it to V_(TH1) and notify the controller.

Now referring back to FIG. 14, step 1415, once Vout drops below V_(TH1)the controller advances to step 1416 where first solid-state switch M1is turned on, second and third solid-state switches M2 and M3 remain onand fourth solid-state switch M4 remains off. Step 1416 is the firstinductor prefluxing state where current in the inductor is linearlyincreased by the application of a voltage at first output terminal 120(Vin) to the inductor before capacitor 170 is charged. The prefluxingstep enables switched regulation circuit 125 circuit to deliverincreased output voltage and/or output current as compared to theswitching configurations described above. In this state the voltage atfirst terminal 120 (Vin) is applied directly across inductor 173.

Now referring to timing diagram 1500, the first prefluxing state isshown at t2. The voltage at second junction 145 rapidly increases to theVin voltage (minus a relatively small voltage drop across M1 and M2) atfirst node 120 shown by trace 1525. Current in inductor 170 (trace 1530)increases rapidly, corresponding to the applied voltage and thecharacteristics of inductor 173. For some embodiments, the voltage at176 may change a relatively small amount compared with the voltageacross the inductor and thus the current may increase substantiallylinear at a rate approximated by Vin−Vout where Vout is the voltage at176. The current in inductor 173 continues until the switch state ischanged, which in one embodiment may be controlled by a timer shown instep 1418. In some embodiments the timer in step 1418 may be a variabletimer that can use a lookup table to adjust according to different loadconditions and demands on switched regulation circuit 125. In furtherembodiments the timer in step 1418 may be variable and may be controlledby a feedback loop based on one or more characteristics of switchedregulation circuit 125. In some embodiments the timer may be adjusted bythe feedback loop to energize inductor 173 with an appropriate amount ofcurrent so that the inductor current resonates to zero just whencapacitor 170 becomes fully charged (discussed in the next step 1420).

In some embodiments, the timer can be made utilizing a current on acapacitor. That current starts charging at the beginning of the prefluxcycle and may be compared to a voltage. When the voltage on thecapacitor reaches a specified voltage the timer indicates that thepreflux cycle should end. In other embodiments this function can be doneutilizing logic gates. Other timers disclosed herein may use similartechniques.

In one embodiment a feedback loop may be used to monitor the current ininductor 173 and adjust the timer. In some embodiments, if the currentis still positive when capacitor 170 becomes fully charged, the timermay be reduced for the next charging cycle. Conversely, if the currentin inductor 173 goes to zero before capacitor 170 becomes fully charged,the timer may be increased for the next cycle. In some embodiments, theloop may use an analog loop. In some embodiments, a DAC can be used toadjust the timer by changing one or more of a current, a capacitor, avoltage threshold on a comparator or a numbers of logic gates.

In some embodiments, instead of a timer for setting the preflux, thecurrent can be monitored during preflux and have the preflux cycles endwhen the current reaches a specified level. That specified level can beadjusted on a cycle by cycle basis to optimize performance. Thatperformance can be to reach a specified average current supplied or sothat the voltage on the capacitor and current in the inductor reacheszero at approximately the same time. Other timers disclosed herein mayuse similar techniques.

In further embodiments that employ a soft braking methodology, discussedin more detail below, the timer can be set to be at least as long asneeded to preflux inductor 173 so the current never reaches zero beforecapacitor 170 is fully charged and soft braking can be used totransition the remaining current in inductor 173. Other embodiments mayuse different techniques to control the timer and are within the scopeof this disclosure.

Now referring back to FIG. 14, after the timer has run, the controlleradvances to step 1420 where first and third solid-state switches M1 andM3 remain on while the second solid-state switch M2 is turned off andthe fourth solid-state switch remains off. Thus, first and thirdsolid-state switches, M1, M3, respectively, are on while second andfourth solid-state switches M2, M4, respectively, are off. In this statethe voltage at first terminal 120 (Vin) is applied directly to secondjunction 145. Capacitor 170 was fully discharged in the step 1405 andnow begins to charge. Capacitor 170 charges with a time constant set bycapacitor 170 and inductor 173 values. Further, as capacitor 170 beginsto charge, current flow in inductor 173 increases as the voltage between145 and the output is positive. Because of the prefluxing operation instep 1416, the current that was already flowing in inductor 173continues to increase, as discussed in more detail below.

Step 1420 is illustrated in timing diagram 1500 (see FIG. 1500) at timet3. Now referring simultaneously to FIGS. 2 and 15, at time t3, secondsolid-state switch 140 (i.e., trace 1510) turns off. The voltage atsecond junction 145 (i.e., trace 1525) begins to decrease. Current ininductor 173 (trace 1530) continues to build as capacitor 170 charges.Voltage in capacitor 170 (trace 1540) increases towards Vin. Ascapacitor 170 becomes charged the current increases in inductor 173(trace 1530) slows and reverses when the voltage at node 145 equals thevoltage at 176 and starts reducing as the capacitor gets fully chargedat t4. Thus, in step 1420 capacitor 170 charges, causing a current toflow in inductor 173, and increasing the voltage at output node 176(Vout). The controller then proceeds to step 1425 (see FIG. 14).

In step 1425, the current in inductor 173 (LI) is detected. In someembodiments the current may be detected as illustrated in FIG. 1 withcomparator 187. In one embodiment comparator 187 monitors current flowthrough first solid-state switch 130 by comparing a voltage differencebetween first terminal 120 and first side 181 of capacitor 170. As thevoltage difference decreases, the current commensurately decreases inboth first solid-state switch 130 and inductor 173. Referring now tostep 1430 in FIG. 14, once current in inductor 173 is approximatelyequal to zero, the controller proceeds to step 1435. In the timingdiagram 1425 and 1430 are shown as discrete steps, while in oneembodiment, the current in Li can be continuously monitored during the1420 conduction cycle. In further embodiments steps 1425 and 1455 can besimilar to steps 356 and 355 in FIG. 9 where both inductor current andcapacitor voltage are monitored.

In step 1435, third solid-state switch M3 turns off and fourthsolid-state switch M4 turns on while second solid-state switch M2remains off. As discussed above, since the transition to step 1435 onlyoccurs when the current in inductor 176 is approximately zero, thetransition to step 1435 may employ zero current switching. Zero currentswitching occurs when the current through the solid-state switch isapproximately zero, before changing the state of the switch. Thisreduces switching losses, reduces input supply noise, and improves theefficiency of switched regulation circuit 125, as discussed in moredetail below.

Continuing to refer to step 1435 in FIG. 14, in some embodiments theswitching transitions may occur simultaneously while in otherembodiments there may be slight delays between switch transitions. Inthe embodiment illustrated in FIG. 15, at t4 switch M4 may have a slightdelay such that it turns on after M3 turns off. This configuration isessentially an off state, where the system is substantially atsteady-state. Other embodiments may have a different off stateconfiguration. In some embodiments only M4 may be on while M1, M2 and M3are off. In further embodiments, all solid-state switches may be in anoff position, while in other embodiments third solid-state switch 150may be the only switch in an on state which connects capacitor 170 toinductor 173. Other off state solid-state switch configurations arewithin the scope of this disclosure.

Step 1435 of FIG. 14 is illustrated in timing diagram 1500 of FIG. 15,at time t4. Now referring simultaneously to FIGS. 2 and 15, at time t4third solid-state switch 150 turns off and fourth solid-state switch 160turns on slightly afterwards. First solid-state switch 130 remains onand second solid-state switch 140 remains off. After the switchingtransitions, second junction 145 (i.e., trace 1525) goes to the voltageat Vout (e.g., it resonates with inductor 173 and parasitic capacitanceat junction 145). Voltage across capacitor 170 (i.e., trace 1540)remains at a charged level and the current in inductor 173 (i.e., trace1530) remains near zero. In step 1440 the voltage at output node 176(Vout) may be detected with comparator 195 (see FIG. 1) as discussedabove in step 1410. In other embodiments, Vout may be detected using adifferent method. As shown in step 1445, the controller advances to step1446 when Vout drops below a second threshold voltage (V_(TH2)).

Now referring to FIG. 14, step 1446, first fourth solid-state switches,M1 and M4 remain on, second solid-state switch M2 turns on, and thirdsolid-state switches M3 remains off. This is the second inductorprefluxing stage where current in inductor 173 is increased by applyingvoltage at first output terminal 120 (Vin) to the inductor before theenergy within capacitor 170 is discharged to the inductor. Theprefluxing step enables switched regulation circuit 125 circuit todeliver increased output voltage and/or output current as compared tothe switching configurations described above. In this state the voltageat first terminal 120 (Vin) is applied directly across inductor 173.

Now referring to timing diagram 1500, the second prefluxing state isshown at t5. The voltage at second junction 145 rapidly increases to theVin voltage at first node 120 shown by trace 1525. Current in inductor170 (trace 1530) increases rapidly, corresponding to the applied voltageand the characteristics of inductor 173. In some embodiment the rate ofcurrent increase can be substantially similar to the rate of currentincrease in the time between t2 and t3. The current in inductor 173continues to increase until the switch state is changed, which in oneembodiment may be controlled by a timer shown in step 1448. In someembodiments the timer in step 1448 may be a variable timer that can usea lookup table to adjust according to different load conditions anddemands on switched regulation circuit 125. In further embodiments thetimer in step 1448 may be variable and may be controlled by a feedbackloop based on one or more characteristics of switched regulation circuit125. In some embodiments the timer may be adjusted by the feedback loopto energize inductor 173 with an appropriate amount of current so thatthe inductor current resonates to zero just when capacitor 170 becomesfully discharged (discussed in the next step 1450). Other timertechniques as discussed herein may be used and are within the scope ofthis disclosure. In some embodiments the timer technique may be the samefor multiple steps within the switching sequence.

In one embodiment a feedback loop may be used to monitor the current ininductor 173 and if the current is still positive when capacitor 170becomes fully discharged, the timer may be reduced for the next chargingcycle. Conversely, if the current in inductor 173 goes to zero beforecapacitor 170 becomes fully discharged, the timer may be increased forthe next cycle. In further embodiments that employ a soft brakingmethodology, discussed in more detail below, the timer can be set to beat least as long as needed to preflux inductor 173 so the current neverreaches zero before capacitor 170 is fully discharged and soft brakingcan be used to transition the remaining current in inductor 173. Otherembodiments may use different techniques to control the timer and arewithin the scope of this disclosure.

Now referring to FIG. 14, step 1450, second and fourth solid-stateswitches M2, M4 remain on and first solid-state switch M1 is turned onwhile third solid-state switch M3 remains off. Capacitor 170 isconnected between inductor 173 and ground 165, allowing the chargestored in the capacitor to discharge through the inductor to load 115(see FIG. 1). As capacitor 170 begins to discharge (with a time constantset by capacitor 170 and inductor 173), current in inductor 173continues to increase and voltage at output node 176 (Vout) increases.This condition is illustrated in timing diagram 1500 in FIG. 15 at timet6.

Now simultaneously referring to FIGS. 2 and 15, at time t6 firstsolid-state switch 130 (i.e., trace 1505) turns off. The voltage atsecond junction 145 (i.e., trace 825) begins to decrease. As capacitor170 resonates with inductor 173, it discharges (i.e., trace 1540)causing current to continue to increase in inductor 173 (i.e., trace1530). This causes the voltage at Vout to increase. As the charge incapacitor 170 is reduced, current in inductor 173 may reverse anddecreases (i.e., trace 1530). The controller then advances to steps 1455and 1460 (see FIG. 14).

In step 1455, the current in inductor 173 is detected. In someembodiments the current may be detected as illustrated in FIG. 1 withcomparator 190. In further embodiments, comparator 190 (see FIG. 1) maybe used to monitor the current through fourth semiconductor switch 160and indirectly through inductor 173, by detecting a voltage differentialbetween ground 165 and second side 191 of capacitor 170. In otherembodiments different methods may be used to detect current in inductor173.

Referring now simultaneously to FIGS. 14 and 15, in step 1460, once thecurrent in inductor 173 is approximately equal to zero, the controllerproceeds back to step 1405, where third solid-state switch M3 is turnedon and second solid-state switch M2 remains on while first solid-stateswitch M1 remains off and fourth solid-state switch M4 is turned off.Thus, M2 and M3 are on while M1 and M4 are off. In some embodiments, M4may be turned on slightly before M3 is turned off. This configurationshorts capacitor 170, repeating the entire switching sequence 1400. Asdiscussed above, since the current in inductor 173 and fourthsolid-state switch M4 is at or near zero during the transition from step1460 to 1405, zero current switching methods may be used to decreaseswitching losses, reduce input supply noise and improve efficiency, asdiscussed in more detail below.

In the particular switching sequence illustrated in FIG. 14, eachsolid-state switch may be configured to turn on and off only once duringeach repetitive switching cycle. Such a sequence may enable improvedefficiency by reducing the number of switching transitions andminimizing switching efficiency losses. In other embodiments, differentswitching configurations and sequences may be used where one or moreswitches may be turned on and off more than once.

Now referring to FIG. 16, timing diagram 1600 is illustrated which is atiming diagram for a similar switching sequence as sequence 1500 in FIG.15, however timing diagram 1600 has two added “soft braking” steps. Asdiscussed above, in some embodiments the timer steps (1418 and 1448 inFIG. 14) may be set to ensure that the prefluxing steps add sufficientenergy to inductor 173 so the current never reaches zero beforecapacitor 170 is fully charged during the charging cycle (or fullydischarged during the discharging cycle) and soft braking can be used totransition the remaining current in inductor 173. Soft braking mayenable a higher current per phase and/or a smaller capacitor 170 perphase as compared to the methodologies discussed above.

In one embodiment a switching sequence where M1, M3 and M4 are on whileM2 is off may be located after step 1430 in FIG. 14. In anotherembodiment a switching sequence where M2, M3 and M4 are on while M1 isoff may be added after step 1460. The first soft braking sequence islabeled as t4 in FIG. 16 and the second soft braking switch sequence islabeled as t8. Other methodologies and switching sequences may be usedand are within the scope of this disclosure.

Now referring to FIG. 17 one embodiment of a preflux timer method 1700will be described. Preflux timer method 1700 is an example of a prefluxtimer that is proportional to one or more of the various characteristicsof the regulator, however other preflux timers may also be proportionalto one or more of the various characteristics of the regulator and mayhave different schematics and/or configurations which are within thescope of this disclosure.

In some embodiments the pre-flux timer may be a digitally programmedtimer based on Vout/Vin (i.e., the duty factor) as described in moredetail below. In further embodiments the accuracy of the timer mayeffect the efficiency of the circuit and thus it may be desirable toimplement methods of increased accuracy.

In one embodiment preflux timer 1700 may use a switched capacitor bank1710 that can be programmed to activate a specific number of capacitorsusing the most significant bits (MSB) of a digital to analog conversion(DAC) code that represents a target output voltage of the circuit. Thatis, the MSB's may represent and be used set the target output voltagefor the circuit. For example, in one embodiment a higher target outputvoltage may correspond to a higher number of active capacitors incapacitor bank 1710 and a lower target output voltage may correspond toa lower number of active capacitors in the capacitor bank.

In some embodiments the active capacitors in capacitor bank 1710 may becharged using a fixed current source 1715 in combination with a variablecurrent source 1720. Variable current source 1715 may be controlled by avariable feedback signal which is an output of a preflux tuningalgorithm 1725. Tuning algorithm 1725 may be configured to adjustvariable current source 1720 based on input from a Cres comparator and acurrent comparator, such as those discussed above. In one embodimenttuning algorithm 1725 may be configured to adjust the variable feedbacksignal to control the variable current source 1720 with a goal of theCres comparator and the current comparator tripping at the same time. Infurther embodiments tuning algorithm 1720 may cause the inductor to beenergized with an appropriate amount of current so current within theinductor resonates to zero at the same time as when the capacitorbecomes fully charged. A timer window 1730 may be set at a value suchthat if the Cres comparator and the current comparator trip within thetimer window time, that tuning algorithm 1725 makes no changes tovariable current source 1720. However, if Cres comparator trips fasteror slower than the current comparator by a time that is greater thantimer window 1730, tuning algorithm 1725 adjusts feedback/variablecurrent 1720 in a way to make Cres comparator closer in time to thecurrent comparator. In some embodiments timer window 1730 may be fixedwhile in other embodiments it may be variable and may be programmable.

In one embodiment tuning algorithm 1725 may use the following steps,while other embodiments may use different steps:

-   -   Step 1: If current comparator trips first, increase the pre-flux        time. Otherwise go to Step 2.    -   Step 2: Start 100 pS timer window after Cres comparator trips.        Go to Step 3.    -   Step 3: If 100 pS timer window expires before the current        comparator trips reduce the pre-flux time. If 100 pS timer        window does not expire before the current comparator trips make        no changes to the preflux time. Go to Step 1.

In some embodiments, capacitor bank 1710 may have a capacitor bankoutput voltage that feeds into a comparator 1735. In one embodimentcomparator 1735 may include a sample and hold function as well as acomparator function and may have a set point that is adjusted with thevariable feedback signal, as discussed above. Comparator 1735 may alsouse a output voltage of the circuit (Vout) as an input to compare withthe capacitor bank output voltage. In one embodiment comparator 1735 maysample the output voltage of the circuit (Vout) when the prefluxoperation begins, then continuously sample the capacitor bank outputvoltage and compare it to the Vout. Once the capacitor bank outputvoltage ramps up and becomes equal to Vout, comparator 1735 may transmita signal to stop the preflux operation.

In one embodiment the sample and hold function may have an auto zerocomparator and may be employed to compare the ramping capacitor bankoutput voltage with the sampled value of Vout. In some embodiments Voutsampling may avoid any active/continuous (destabilizing) feedback fromVout on the timer calculation since in some embodiments the preflux Voutmay ramp up very fast. The output of comparator 1735 may be used to senda signal to stop the inductor prefluxing operation.

Thus, in some embodiments preflux timer 1700 may have three variables tocontrol the preflux time including, 1) the tuning algorithm 1725, 2) theDAC MSB setting (i.e. the target output voltage) and 3) the actualoutput voltage of the circuit (Vout). In further embodiments one or acombination of these variables may be used. For example in oneembodiment only the DAC MSB setting may be used to adjust the targetoutput voltage and the tuning algorithm may have a fixed current (asopposed to a variable current) and the Vout may use a fixed referencevoltage (as opposed to the actual Vout voltage).

Now referring to FIG. 18 another embodiment of a preflux timer method1800 will be described. Preflux timer method 1800 is similar to method1700 however method 1800 is a simplified version removing theprogrammable capacitor bank and the sample and hold functions. Similarto preflux timer method 1700, preflux timer method 1800 is alsoproportional to one or more of the various characteristics of theregulator.

In one embodiment preflux timer 1800 may use a reference generator 1810to generate a reference voltage from two inputs. The first input may bethe DAC/MSBs described above that represents a target output voltage ofthe circuit. The second input may be a comparator set point that uses avariable input from a feedback loop controlled by the output of apreflux tuning algorithm 1825. Tuning algorithm 1825 may be configuredto adjust the feedback based on input from a Cres comparator and acurrent comparator, such as those discussed above. In one embodimenttuning algorithm 1825 may be configured to adjust the feedback with agoal of the Cres comparator and the current comparator tripping at thesame time. In further embodiments tuning algorithm 1820 may cause theinductor to be energized with an appropriate amount of current socurrent within the inductor resonates to zero at the same time as whenthe capacitor becomes fully charged. A timer window 1830 may be set at avalue such that if the Cres comparator and the current comparator tripwithin the timer window time, that tuning algorithm 1825 makes nochanges to the feedback. However, if Cres comparator trips faster orslower than the current comparator by a time that is greater than timerwindow 1830, tuning algorithm 1825 adjusts the feedback in a way to makeCres comparator closer in time to the current comparator. In someembodiments timer window 1830 may be fixed while in other embodiments itmay be variable and may be programmable.

In some embodiments, reference voltage generator 1810 may have areference voltage output that feeds into a comparator 1835. Comparator1835 may also use a voltage across one of the solid-state switchesdescribed above in FIG. 1 such as M1, M2, M3 or M4. In one embodimentthe voltage across M1 (V_(M1)) may be used as an input to comparator1835 to compare with reference generator 1810 voltage. In someembodiments the first solid-state switch M1 may have a characteristicresistance so the input (e.g., V_(M1)) is proportional to the current inthe inductor 173 (see FIG. 1) when M1 is in an on state allowing currentto flow through the inductor. The output of comparator 1835 may be usedto send a signal to stop the inductor prefluxing operation.

In further embodiments a comparator to monitor a voltage across a one ofthe solid-state switches described above in FIG. 1 such as M1, M2, M3 orM4 may be made using a ratiometric circuit. For example, in oneembodiment a voltage across a relatively large M1 solid-state transistormay be monitored by fabricating a scaled down solid-state transistor M1x on the same die. In some embodiments, for example, M1 x may be oneone-thousandth the size of M1 and M1 x may have the same gate voltageand source voltage as M1. The current of M1 x may go to a current sinkand a current comparator may be used to monitor the current through M1 xas compared to a reference current. Since M1 x is one one-thousandth thesize of M1 the reference current may be set to one one-thousandth of thedesired current in M1 so the comparator trips when the desired currentin M1 is reached. In one embodiment second junction 145 (see FIG. 1) canbe used as the reference input to the comparator. This may enable thecopied current in M1 x to match the current in M1. Note that in someembodiments the M1 solid-state switch may be in linear conduction (notsaturation), therefore M1 x may need the same gate drive voltage andsame drain source voltage to copy the current accurately. In otherembodiments a different ratio or other comparator methods may be usedand are within the scope of this disclosure.

Regulator with Continuous Current

In other embodiments switched regulation circuit 125 (see FIG. 2) can beconfigured to provide continuous current and/or an increase in currentto load 115 by maintaining the current in inductor 173 above zero, asdescribed in more detail below.

Now referring simultaneously to FIGS. 2, and 19-26 an example switchingsequence and timing diagram for an embodiment of switched regulationcircuit 125 (see FIG. 2) with continuous and/or increased current isillustrated. More specifically, FIG. 2 illustrates a simplifiedschematic of switched regulation circuit 125; FIG. 19 illustrates anexample switching sequence 1900 having sequential steps 1905 through1940 for the four switches in switched regulation circuit 125; FIG. 20illustrates an example timing diagram showing the control signalsdelivered to each of the four solid-state switches as well as thecurrent within inductor 173 (I_(L)), and the voltage at second junction145 (V₁₄₅) during switching sequence 1900; and FIGS. 21-26 illustratesimplified circuit schematics of each of the six different solid-stateswitch configurations described in switching sequence 1900. In FIGS.21-26 solid-state switches that are in an on state are depicted withsolid lines and solid-state switches that are in an off state aredepicted with dashed lines. The switching sequence illustrated in FIG.19 is for example only and other switching sequences, timings andconfigurations are within the scope of this disclosure.

Now referring to FIG. 19, switching sequence 1900 having sequentialsteps 1905 through 1940 is illustrated. In step 1905, first, second andthird solid-state switches M1, M2 and M3, respectively, are controlledto be in an on state and fourth solid-state switch M4 is controlled tobe in an off state. A simplified schematic of switched regulationcircuit 125 in step 1905 is illustrated in FIG. 21. Step 1905 is a firstinductor prefluxing state where current in inductor 173 (see FIG. 2) isincreased at a substantially linear rate by the application of the inputvoltage at first terminal 120 (Vin) across the inductor, at a timebefore capacitor 170 is charged.

Example currents and voltages within switched regulation circuit 125 forstep 1905 are illustrated in timing diagram 2000 (see FIG. 20). Thelogic levels for solid-state switch control signals M1, M2, M3, M4 areindicated by traces 2005, 2010, 2015 and 2020, respectively. A highlogic level (sometimes noted as 1) indicates the switch (or compositeswitch) is in an on state, and a low logic level (sometimes noted as 0)indicates the switch is in an off state.

Timing diagram 2000 illustrates that first step 1905 occurs at time t1.At time t1, trace 2005 shows that a high logic level control signal isapplied to first solid-state switch 130, placing it in an on state.Trace 2010 illustrates that at time t1 a high logic level control signalis applied to second solid-state switch 140, placing it in an on state.Trace 2015 illustrates that at time t1 a high logic level control signalis applied to third solid-state switch 150, placing it in an on state.Trace 2020 illustrates that at time t1 a low logic level control signalis applied fourth solid-state switch 160, placing it in an off state.

Continuing to refer to timing diagram 2000, at t1 a voltage at secondjunction 145 (see FIG. 2) is illustrated by trace 2025 and issubstantially equivalent to the Vin voltage (minus a relatively smallvoltage drop across M1 and M2) at first node 120. Current in inductor170 (I_(L) trace 2030) increases rapidly, corresponding to the appliedvoltage and the characteristics of inductor 173. For some embodiments,the voltage at node 176 (see FIG. 2) may change a relatively smallamount compared with the voltage across the inductor and thus thecurrent may increase substantially linear at a rate approximated by(Vin−Vout)/L where Vout is the voltage at node 176. The current ininductor 173 continues to increase while in this switch state, theduration of which may be controlled by a timer, shown in step 1910 as adelay.

In some embodiments the timer in step 1910 can be fixed while in otherembodiments it can be a variable timer. In one example the variabletimer can use a lookup table to adjust according to different loadconditions and demands on switched regulation circuit 125. Morespecifically, in some embodiments the timer can be set proportional to a“duty factor” (e.g., Vout/Vin) such that a longer amount of time isselected when a higher Vout is required. In further embodiments thetimer in step 1910 can be controlled by a feedback loop based on one ormore characteristics of switched regulation circuit 125. In someembodiments the timer may be adjusted by the feedback loop to energizeinductor 173 with an appropriate amount of current so that the inductorcurrent resonates to a predetermined current when the first resonatingstate is engaged (discussed in the next step 1915). In furtherembodiments the timer can use a comparator that compares the current inthe inductor to a programmable current threshold.

In other embodiments, the timer can be made utilizing a current on acapacitor wherein the current starts charging at the beginning of thepreflux cycle and may be compared to a predetermined voltage. When thevoltage on the capacitor reaches a specified voltage the timer indicatesthat the preflux cycle should end. In other embodiments the timerfunction can be performed utilizing logic gates.

In some embodiments, instead of a timer for setting the amount ofpreflux, the current in the inductor can be monitored during preflux(e.g., step 1905) and the preflux cycle can be set to end when thecurrent reaches a specified level. That specified current level can beadjusted on a cycle by cycle basis to optimize performance. Other timertechniques and timer architectures can be used and are within the scopeof this disclosure.

Now referring to FIG. 19, after the delay in step 1910, the controlleradvances to step 1915 where first and third solid-state switches M1 andM3 remain on while the second solid-state switch M2 is turned off andthe fourth solid-state switch M4 remains off. Thus, first and thirdsolid-state switches, M1, M3, respectively, are on while second andfourth solid-state switches M2, M4, respectively, are off. A simplifiedschematic of switched regulation circuit 125 in step 1915 is illustratedin FIG. 22. This state couples capacitor 170 in series with inductor 173and the voltage at first terminal 120 (Vin) is applied directly tosecond junction 145. Capacitor 170 now begins to charge. Capacitor 170charges with a time constant set by capacitor 170 and inductor 173values. Further, as capacitor 170 begins to charge, current flow ininductor 173 continues to increase as the voltage between secondjunction 145 and the output is positive. Because of the prefluxingoperation in step 1905, the current that was already flowing in inductor173 continues to increase, as discussed in more detail below.

Step 1915 is illustrated in timing diagram 2000 (see FIG. 20) at timet2. Now referring simultaneously to FIGS. 2 and 20, at time t2, secondsolid-state switch 140 (i.e., trace 2010) turns off. The voltage atsecond junction 145 (i.e., trace 2025) begins to decrease. Current ininductor 173 (trace 2030) continues to build as capacitor 170 charges.Voltage in capacitor 170 increases towards Vin. As capacitor 170 becomescharged the current in inductor 173 (trace 2030) peaks, then begins todecrease when the voltage at node 145 equals the voltage at node 176 andcontinues to decrease towards time t3. Thus, in step 1915, capacitor 170charges, causing a current to flow in inductor 173, and increasing thevoltage at output node 176 (Vout). When capacitor 170 is fully chargedto the voltage at (Vin) 120, the controller proceeds to step 1920 (seeFIG. 19) which is a first “soft braking” configuration that can be usedto transition the current remaining in inductor 173. Soft braking canenable a higher current per phase and/or a smaller capacitor 170 perphase as compared to the methodologies discussed above and as explainedin more detail below.

In the first soft braking configuration (step 1920) first, third andfourth solid-state switches M1, M3 and M4, respectively, are on whilesecond solid-state switch M2 is turned off. A simplified schematic ofswitched regulation circuit 125 in step 1920 is illustrated in FIG. 23.In this state inductor 173 is coupled to Vin (node 120) throughcapacitor 170 and also to ground 165 through third and fourthsolid-state switches, M3 and M4, respectively, allowing the residualcurrent in the inductor to continue to decrease down to a non-zerominimum current (Imin).

Step 1920 is illustrated in timing diagram 2000 (see FIG. 20) at timet3. Now referring simultaneously to FIGS. 2 and 20, at time t3, fourthsolid-state switch 160 (i.e., trace 2020) turns on adding a path betweeninductor 173 and ground 165. The voltage at second junction 145 (i.e.,trace 2025) remains at the ground potential and current in inductor 173(trace 2030) continues to decrease as the inductor dissipates its storedenergy. Current in inductor 173 continues to decrease to a predeterminedminimum current (Imin) that is non-zero in this particular embodiment.In some embodiments the minimum current (Imin) can be between 10milliamps and 50 amperes, while in other embodiments it can be between100 milliamps and 1 ampere and in another embodiment it can be between200 milliamps and 400 milliamps. The controller then proceeds to step1925 (see FIG. 19) that is a second prefluxing state that can be used toincrease current flowing through inductor 173.

Now referring to FIG. 19, in step 1925 first fourth solid-stateswitches, M1 and M4 remain on, second solid-state switch M2 turns on,and third solid-state switches M3 remains off. A simplified schematic ofswitched regulation circuit 125 in step 1925 is illustrated in FIG. 24.This is the second inductor prefluxing stage where current in inductor173 is increased at a substantially linear rate by applying voltage atfirst output terminal 120 (Vin) to the inductor. In this state thevoltage at first terminal 120 (Vin) is applied directly across inductor173.

Now referring to timing diagram 2000, the second prefluxing state (step1925) is shown at t4. The voltage at second junction 145 rapidlyincreases to the Vin voltage at first node 120 shown by trace 2025.Current in inductor 170 (trace 2030) increases rapidly, corresponding tothe applied voltage and the characteristics of inductor 173. In someembodiments the rate of current increase can be substantially similar tothe rate of current increase in the time between t1 and t2. The currentin inductor 173 continues to increase until the switch state is changed,which in one embodiment, may be controlled by a delay shown in step 1930that can be controlled by a timer, as discussed above.

Now referring to FIG. 19, in step 1935 fourth solid-state switch M4remains on and second solid-state switch M2 is turned on while first andthird solid-state switches M1, M3, respectively, remain off. Asimplified schematic of switched regulation circuit 125 in step 1935 isillustrated in FIG. 25. Capacitor 170 is connected between inductor 173and ground 165, allowing the charge stored in the capacitor to dischargethrough the inductor to load 115 (see FIG. 1). As capacitor 170 beginsto discharge (with a time constant set by capacitor 170 and inductor173), current in inductor 173 increases. This condition is illustratedin timing diagram 2000 in FIG. 20 at time t5 showing the voltage atsecond junction 145 (i.e., trace 2025) at a voltage that is close to thevoltage at Vin (120) as it is connected to fully charged capacitor 170.As capacitor 170 resonates with inductor 173, it discharges causingcurrent to increase in inductor 173 (i.e., trace 2030). The increase incurrent causes the voltage at Vout (node 176) to increase. As the chargestored in capacitor 170 is reduced, current in inductor 173 peaks(Ipeak), then begins to decrease (trace 2030).

The controller then proceeds to step 1940 (see FIG. 19) which is asecond “soft braking” configuration that can be used to transition theremaining current in inductor 173. Soft braking can enable a highercurrent per phase and/or a smaller capacitor 170 per phase as discussedabove.

More specifically, in step 1940 second, third and fourth solid-stateswitches M2, M3 and M4, respectively, are on while first solid-stateswitch M1 is turned off. A simplified schematic of switched regulationcircuit 125 in step 1935 is illustrated in FIG. 26. In this stateinductor 173 is coupled to ground 165 through third and fourthsolid-state switches, M3 and M4, respectively, allowing the residualcurrent in the inductor to continue to decrease down to a non-zerominimum current (Imin).

Step 1940 is illustrated in timing diagram 2000 (see FIG. 20) at timet6. Now referring simultaneously to FIGS. 2 and 20, at time t6, thirdsolid-state switch 150 (i.e., trace 2015) turns on adding a path betweeninductor 173 and ground 165. The voltage at second junction 145 (i.e.,trace 2025) remains at the ground potential and current in inductor 173(trace 2030) continues to decrease as the inductor dissipates its storedenergy. Current in inductor 173 continues to decrease to a predeterminedminimum current (Imin) that is non-zero in this particular embodiment.The controller then returns to step 1905 (see FIG. 19) which is thefirst prefluxing state that can be used to increase current flowingthrough inductor 173.

Timing diagram 2000 in FIG. 20 is for illustration only and is oneexample of the function of circuit 125 (see FIG. 2) operating with anon-zero inductor current. Other switching algorithms, control functionsand features can be implemented without departing from this disclosure.To control the duration of any of steps 1905-1940 illustrated in FIG. 19any type of timer or control circuit can be used, including thosedisclosed herein. For example, in some embodiments a comparator can beused to compare output voltage (Vout) to a commanded voltage. If theoutput voltage is too low the controller can shorten the soft brakeduration and start the next preflux step early, leading to a higheroutput voltage and higher average output current delivered to load 115(see FIG. 1). This control algorithm can also provide a relatively fastresponse time to loads having high transient voltage requirements. Infurther embodiments a multi-phase architecture can be employed wheremultiple switched regulation circuits 125 (see FIG. 2) are used togetherto provide power to load 115.

In further embodiments alternative switching sequences 1900 can be usedto provide additional features and functions of switched regulationcircuit 125 (see FIG. 2). For example, wait states can be added afterfirst and second soft brake steps (steps 1920 and 1940, respectively) toprovide light load performance. More specifically, when load 115 (seeFIG. 1) requires a reduced amount of current and/or voltage, after firstsoftbrake (step 1920) a wait state can be commanded where first andfourth solid-state switches, M1 and M4, respectively are on and secondand third solid-state switches, M2 and M3 are off. This essentiallyhalts current flow through circuit 125 to load 115 (see FIG. 1) untilthe subsequent preflux step 1925 is commanded. Similarly, after secondsoft brake (step 1940) a second wait state can be commanded where secondand third solid-state switches, M2 and M3, respectively, are on andfirst and fourth solid-state switches, M1 and M4, respectively, are off.This state essentially halts current flow through circuit 125 until thesubsequent preflux step 1905 is commanded.

Now referring to FIG. 27 a switching sequence 2700 is illustrated thatdepicts additional example switching sequences that can be used toprovide additional features and functions of switched regulation circuit125 (see FIG. 2). Many of the switch configurations in switchingsequence 2700 are similar to the switch configurations in FIG. 19, wherelike numbers refer to similar configurations (e.g., switch configuration1905 in FIG. 19 corresponds to switch configuration 1905 in FIG. 27),however switching sequence 2700 adds two additional switchconfigurations (step 2723) and (step 2743) that are waiting states thatallow the switched regulation circuit 125 to operate under light loadconditions. As further illustrated in switching sequence 2700 there arealso several alternative switching sequences, identified by lines 2750,2755, 2760, 2765, 2770, 2775, 2780 and 2785, each of which will bediscussed in more detail below.

In one example, switching sequence 2700 includes steps (1915, 1920,2723, 1935, 1949 and 2743) and thus first and second preflux steps 1905,1925, respectively, are not performed. Instead of following thesequential switching sequence, in this example, switching sequence 2700follows paths 2760 and 2775, skipping first and second preflux steps1905, 1925, respectively. The omission of first and second preflux steps1905, 1925, respectively, can result in a reduction of the currentflowing through inductor 173. This sequence can be used to deliver lowercurrent and/or voltage to load 115 (see FIG. 1). In some embodimentseither first preflux step 1905 or second preflux step 1925 can beskipped independently of each other to provide a relatively fastresponse to changing load requirements.

In another example, switching sequence 2700 includes steps (1905, 1915,2723, 1925, 1935 and 2743) and thus first and second soft brake steps1920, 1940, respectively, are not performed. Instead of following thesequential switching sequence, in this example switching sequence 2700follows paths 2755 and 2765, skipping first and second soft brake steps1920, 1940, respectively. The omission of first and second soft brakesteps 1920, 1940, respectively, can be used in embodiments wherecapacitor 170 (see FIG. 2) is relatively large and becomes fullycharged/discharged at the same time the current in inductor 173 nearszero. Therefore, since the capacitor can “absorb” substantially all ofthe energy from the inductor, there is little to no current left in theinductor at the end of the resonating steps for the soft brake steps todissipate. In a similar example, switching sequence 2700 can skip notonly first and second soft brake steps 1920, 1940, respectively, but canalso skip first and second wait steps, 2723 and 2743, respectively. Inthis case the loading conditions on switched regulation circuit 125 aresufficient that the controller does not need to lower output currentand/or voltage by using waiting states (steps 2723 and 2743). In thisexample switching sequence 2700 follows paths 2780 and 2785, skippingsteps 1920, 2723, 1940 and 2743.

In another example, switching sequence 2700 can be used to change theoperation of switched regulation circuit 125 (see FIG. 2) between acontinuous current output mode and a discontinuous current output modeof operation based on one or more parameters of switched regulationcircuit 125. More specifically, in some embodiments, during operationthe demands of load 115 can change and controller 180 can respond byincreasing or decreasing the output current of switched regulationcircuit 125 by altering switching sequence 2700, as described in moredetail below.

In some embodiments under light load conditions, controller 180 can skipone or more steps in switching sequence 2700 during the continuousuninterrupted operation of switched regulation circuit 125. In oneexample an autonomous transition to an alternative switching sequencecan occur during first and/or second softbrake steps, steps 1920 and1940, respectively. The transition can be the result of the voltage at(Vout) 176 being above or below a predetermined threshold voltage or inresponse to any parameter of the circuit.

In one example the voltage at (Vout) 176 is above a predeterminedthreshold voltage, (e.g., the load does not need additional power) andcontroller 180 seamlessly transitions switching sequence 2700 to adiscontinuous current mode of operation. In some embodiments adiscontinuous current mode results when controller 180 ends first and/orsecond softbrake steps, steps 1920 and 1940, respectively when thecurrent in inductor 173 reaches zero (e.g., a discontinuous currentoutput). Controller 180 can further proceed to first and/or second waitstates, steps 2723 and 2743, respectively until the controller 180determines that load 115 requires more power (e.g. (Vout) 176 dropsbelow the predetermined threshold voltage).

In some embodiments if during first and/or second softbrake steps, steps1920 and 1940, respectively, the voltage at (Vout) 176 is below thepredetermined threshold voltage, (e.g., the load requires additionalpower) controller 180 can truncate the duration of first and/or secondsoftbrake steps, steps 1920 and 1940, respectively, and advance to firstand/or second preflux states, steps 1905 and 1925, respectively, toincrease the output current and/or transition to a continuous currentmode of operation.

In further embodiments controller 180 can shorten or lengthen theduration of any step within switching sequence 2700 in response to oneor more parameters of switched regulation circuit 125. As anotherillustrative example, if the current in inductor 173 is decreasing whileswitched regulation circuit 125 is in first and/or second resonatingmodes, steps 1915 and 1935, respectively, and load 115 requiresadditional power, controller 180 can end the step early and cantransition to first and/or second preflux states, steps 1905 and 1925,respectively, to increase the output current and/or transition to acontinuous current mode of operation.

In further embodiments switched regulation circuit 125 can use a firstand a second levels of current within inductor 173 to control operationof the operation of the circuit. More specifically a voltage at the loadcan be regulated by repetitively (1) charging the capacitor causing anincrease in current flow in the inductor followed by a decrease incurrent flow in the inductor and before the current flow in the inductorreaches a first level, (2) discharging the capacitor causing an increasein current flow in the inductor followed by a decrease in current flowin the inductor and before the current flow in the inductor reaches asecond level, repeating (1). The first and the second levels can be setby controller 180 or any other circuit and are based on one or moreelectrical characteristics of switched regulation circuit 125. In someembodiments first and second levels can be substantially equal to 0amperes however in other embodiments they may have a positive or anegative value. In further embodiments the first and the second levelscan have different values.

Other switching sequences are within the scope of this disclosure andthe switch configurations shown in FIG. 27 do not need to be performedin any particular order or for a particular time. Further, the switchconfigurations shown in FIG. 27 do not indicate that the same sequencemust be repetitively performed during operation of switched regulationcircuit 125 (see FIG. 2). More specifically, because of the flexibilityof the design of switched regulation circuit 125 (see FIG. 2) theswitching sequence can be modified at any time by controller 180 (seeFIG. 1) as illustrated by, but not limited to lines 2750, 2755, 2760,2765, 2770, 2775, 2780 and 2785. That is, based on the inputs tocontroller, controller 180 can immediately change switching sequences,for example by skipping first softbrake (step 1920) and proceeding tofirst wait state (step 2723), proceeding to second preflux (step 1925),proceeding to second resonating (step 1935) and proceeding to secondsoftbrake (step 1940). Thus, just because the controller skipped thefirst softbrake (step 1920) it does not necessarily have to skip secondsoftbrake (step 1940).

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense. The sole and exclusive indicator of the scope of the invention,and what is intended by the applicants to be the scope of the invention,is the literal and equivalent scope of the set of claims that issue fromthis application, in the specific form in which such claims issue,including any subsequent correction.

1. A power conversion circuit comprising: a first terminal; a firstsolid-state switch having a pair of first switch terminals and a firstcontrol terminal, the pair of first switch terminals connected betweenthe first terminal and a first junction; a second solid-state switchhaving a pair of second switch terminals and a second control terminal,the pair of second switch terminals connected between the first junctionand a second junction; a third solid-state switch having a pair of thirdswitch terminals and a third control terminal, the pair of third switchterminals connected between the second junction and a third junction; afourth solid-state switch having a pair of fourth switch terminals and afourth control terminal, the pair of fourth switch terminals connectedbetween the third junction and a ground; a capacitor coupled between thefirst junction and the third junction, and an inductor coupled betweenthe second junction and a load; and a controller transmitting controlsignals to control the first, second, third and fourth solid-stateswitches through the first, second, third and fourth control terminals,respectively, such that a voltage at the load is regulated byrepetitively (1) charging the capacitor causing an increase in currentflow in the inductor followed by a decrease in current flow in theinductor and before the current flow in the inductor stops SUBSTANTIALLY0, (2) discharging the capacitor causing an increase in current flow inthe inductor followed by a decrease in current flow in the inductor andbefore the current flow in the inductor stops, repeating (1).
 2. Thepower conversion circuit of claim 1 further comprising generating afirst preflux condition in the inductor before (1).
 3. The powerconversion circuit of claim 2 wherein during the first preflux conditionthe first and the second solid-state switches are in an on state.
 4. Thepower conversion circuit of claim 1 further comprising generating asecond preflux condition in the inductor before (2).
 5. The powerconversion circuit of claim 4 wherein during the second prefluxcondition the second and the fourth solid-state switches are in an onstate.
 6. The power conversion circuit of claim 1 wherein after thedecrease in current flow the inductor in (1) the first, the third andthe fourth solid-state switches are in an on state.
 7. The powerconversion circuit of claim 1 wherein after the decrease in current flowthe inductor in (2) the second, the third and the fourth solid-stateswitches are in an on state.
 8. The power conversion circuit of claim 1wherein when repetitively performing (1) and (2) a continuous currentflows through the inductor.
 9. The power conversion circuit of claim 1wherein the controller allows the current flow in the inductor to stopin (1) and in response controls the first and the fourth solid-stateswitches into an on-state and the second and third solid-state switchesinto an off state.
 10. The power conversion circuit of claim 9 whereinthe controller controls the first and the fourth solid-state switchesinto an on-state and the second and third solid-state switches into anoff state in response to a voltage at the load being above apredetermined threshold voltage.
 11. The power conversion circuit ofclaim 1 wherein the controller allows the current flow in the inductorto stop in (2) and in response controls the second and the thirdsolid-state switches into an on-state and the first and fourthsolid-state switches into an off state.
 12. The power conversion circuitof claim 1 disposed on a unitary semiconductor die that includes theload.
 13. A power conversion circuit comprising: a first terminal; afirst solid-state switch having a pair of first switch terminals and afirst control terminal, the pair of first switch terminals connectedbetween the first terminal and a first junction; a second solid-stateswitch having a pair of second switch terminals and a second controlterminal, the pair of second switch terminals connected between thefirst junction and a second junction; a third solid-state switch havinga pair of third switch terminals and a third control terminal, the pairof third switch terminals connected between the second junction and athird junction; a fourth solid-state switch having a pair of fourthswitch terminals and a fourth control terminal, the pair of fourthswitch terminals connected between the third junction and a ground; anda capacitor coupled between the first junction and the third junction,and an inductor coupled between the second junction and a load; whereinthe first, second, third and fourth solid-state switches regulate avoltage at the load by repetitively (1) charging the capacitor causingan increase in current flow in the inductor followed by a decrease incurrent flow in the inductor and before the current flow in the inductorreaches a first level, (2) discharging the capacitor causing an increasein current flow in the inductor followed by a decrease in current flowin the inductor and before the current flow in the inductor reaches asecond level, repeating (1).
 14. The power conversion circuit of claim13 wherein the first and the second levels are substantially 0 amperes.15. The power conversion circuit of claim 13 further comprisinggenerating a first preflux condition in the inductor before (1).
 16. Thepower conversion circuit of claim 13 further comprising generating asecond preflux condition in the inductor before (2).
 17. The powerconversion circuit of claim 13 wherein when repetitively performing (1)and (2) a continuous current flows through the inductor.
 18. The powerconversion circuit of claim 13 wherein in response to a voltage at theload being above a predetermined threshold voltage the controller allowsthe current flow in the inductor to stop in (1).
 19. The powerconversion circuit of claim 13 wherein the first, second, third andfourth solid-state switches are disposed on a unitary semiconductor diethat is attached to a substrate having a plurality of contacts forforming electrical connections to a circuit board.
 20. A method ofoperating a power conversion circuit to deliver power to a load, themethod comprising: supplying power to the power conversion circuit witha power supply connected to a first terminal, the power conversioncircuit comprising: a first solid-state switch having a pair of firstswitch terminals and a first control terminal, the pair of first switchterminals connected between the first terminal and a first junction; asecond solid-state switch having a pair of second switch terminals and asecond control terminal, the pair of second switch terminals connectedbetween the first junction and a second junction; a third solid-stateswitch having a pair of third switch terminals and a third controlterminal, the pair of third switch terminals connected between thesecond junction and a third junction; a fourth solid-state switch havinga pair of fourth switch terminals and a fourth control terminal, thepair of fourth switch terminals connected between the third junction anda ground; a capacitor coupled between the first junction and the thirdjunction, and an inductor coupled between the second junction and theload; and a controller that controls on and off states of the first,second, third and fourth solid-state switches; and controlling the onand off states of the first, the second, the third and the fourthsolid-state switches, such that a voltage at the load is regulated byrepetitively (1) charging the capacitor causing an increase in currentflow in the inductor followed by a decrease in current flow in theinductor and before the current flow in the inductor reaches a firstlevel, (2) discharging the capacitor causing an increase in current flowin the inductor followed by a decrease in current flow in the inductorand before the current flow in the inductor reaches a second level,repeating (1).